Materials comprising carbon-embedded iron nanoparticles, processes for their manufacture, and use as heterogeneous catalysts

ABSTRACT

The present invention relates to catalytically active material, comprising grains of non-graphitizing carbon with iron nanoparticles dispersed therein, wherein d p , the average diameter of iron nanoparticles in the non-graphitizing carbon grains, is in the range of 1 nm to 20 nm, D, the average distance between iron nanoparticles in the non-graphitizing carbon grains, is in the range of 2 nm to 150 nm, and ω, the combined total mass fraction of metal in the non-graphitizing carbon grains, is in the range of 30 wt % to 70 wt % of the total mass of the non-graphitizing carbon grains, and wherein d p , D and ω conform to the following relation: 4.5 d p /ω&gt;D≥0.25 d p /ω. The present invention, further, relates to a process for the manufacture of material according to the invention, as well as its use as a catalyst.

BACKGROUND

The present invention relates to a material, comprising grains ofnon-graphitizing carbon with iron nanoparticles dispersed therein. Thematerial according to the invention is catalytically active in a varietyof chemical reactions and can be obtained by a facile procedure.

The carbon phase of the invention is largely amorphous and does notappear to be activated carbon, carbon black, graphite, graphitizedcarbon black or paracrystalline carbon.

THE PRIOR ART

Significant prior art-efforts have been directed at synthesizingtransition metal nanoparticles, including transition metal nanoparticleswith catalytic activity in particular. As nanoparticles per se, however,cannot be employed in most heterogeneously catalyzed processes, furtherendeavors were conducted to develop materials containing transitionmetal nanoparticles attached to suitable supports, substrates or wafers.Prior art approaches for this purpose were mostly based uponimpregnation or chemical vapor deposition of metal precursors ontoporous or mesoporous supports (Sietsma, Jelle R. A., et al. “Highlyactive cobalt-on-silica catalysts for the fischer-tropsch synthesisobtained via a novel calcination procedure.” Studies in Surface Scienceand Catalysis (2007); Van Deelen, T. W., et al. “Assembly and activationof supported cobalt nanocrystal catalysts for the Fischer—Tropschsynthesis.” Chemical Communications (2018).) or using well definedligands for the metal species and applying high temperature treatment(Westerhaus, Felix A., et al. “Heterogenized cobalt oxide catalysts fornitroarene reduction by pyrolysis of molecularly defined complexes”Nature Chemistry (2013); Banerjee, Debasis, et al. “Convenient and MildEpoxidation of Alkenes Using Heterogeneous Oxide Catalysts” AngewandteChemie, International Edition (2014).) Interactions of nanoparticles andsupport, however, were found to bring about significant limitations(Oschatz, M., et al. “Effects of calcination and activation conditionson ordered mesoporous carbon supported iron catalysts for production oflower olefins from synthesis gas” Catalysis Science & Technology(2016).) Prior art procedures, in particular, failed to yield materialsexhibiting high dispersion and uniform coordination of transitionmetal-/metal oxide-nanoparticles in combination with high metal content.Most prior art transition metal nanoparticle materials in fact, exhibitrather low active metal concentrations of less than 20 wt % as a resultof clustering and a corresponding loss of dispersion of metal particlesat higher metal concentrations (Hernandez Mejia, Carlos, Tom W. vanDeelen and Krijn P de Jong. “Activity enhancement of cobalt catalysts bytuning metal-support interactions” Nature Communications (2018);Oschatz, M., et al. “Effects of calcination and activation conditions onordered mesoporous carbon supported iron catalysts for production oflower olefins from synthesis gas.” Catalysis Science & Technology(2016)). In view of the fact that materials exhibiting high dispersionand uniform coordination of transition metal-/metal oxide-nanoparticlesin combination with high metal content are currently unavailable whilesuch properties are considered as desirable, in order to obtain materialwith high catalytic activity, there is a need in the art for providingsuch materials as well as processes for their manufacture.

The present invention provides materials exhibiting the propertiesdesired and a facile process for their manufacture.

THE PRESENT INVENTION

The present invention relates to catalytically active material,comprising grains of non-graphitizing carbon with iron nanoparticlesdispersed therein,

-   -   wherein    -   dp, the average diameter of iron nanoparticles in the        non-graphitizing carbon grains, is in the range of 1 nm to 20        nm,    -   D, the average distance between iron nanoparticles in the        non-graphitizing carbon grains, is in the range of 2 nm to 150        nm, and    -   ω, the combined total mass fraction of metal in the        non-graphitizing carbon grains, is in the range of 30 wt % to 70        wt % of the total mass of the non-graphitizing carbon grains,    -   wherein d_(p) and D are measured by TGZ-TEM as described herein,    -   and wherein    -   dp, D and ω conform to the following relation:

4.5dp/ω>D≥0.25dp/ω.

Material according to the present invention can be obtained by a processcomprising the following steps:

-   -   (a) providing an aqueous solution comprising metal precursor and        organic carbon source,        -   wherein the metal precursor comprises one or a combination            of more than one organic, at least partially water soluble,            salts of iron, and        -   wherein the organic carbon source is one or a combination of            more than one saturated, aliphatic di-, tri-, or            polycarboxylic acids,    -   (b) spray drying or freeze drying the aqueous solution of metal        precursor and organic carbon source and, thus, obtaining        intermediate product P,    -   (c) thermo-treating intermediate product P at a temperature in        the range from 200° C. to 380° C.

As a result of research underlying the present invention it was foundthat grains of non-graphitizing carbon with iron nanoparticles dispersedtherein, can be obtained from aqueous solutions of metal precursors andorganic carbon sources by combining

-   -   (i) spray drying or freeze drying of the aqueous solution, with    -   (ii) thermal treatment at moderate temperatures of the        intermediate obtained from step (i).

The final product was found to exhibit catalytic activity in a varietyof chemical reactions. In the context of the present invention, anymaterial or substance lowering the activation energy of a chemicalreaction and thus increasing its rate at a particular temperature,without being consumed by the catalyzed reaction itself, is consideredas catalytically active.

Variation of process conditions and examination of the materialsobtained, uncovered process conditions and material properties asclaimed herein.

It was found that forming aqueous solutions of metal precursors andorganic carbon sources in glass beakers and slowly drying thesesolutions overnight in a drying cabinet did not yield intermediateproducts that could be transformed into grains of non-graphitizingcarbon with iron nanoparticles dispersed therein by thermal treatment atmoderate temperatures. Specifically, it was found that if the dryingprocess was performed too slowly, significant decomposition ofpolycarboxylic acids and formation of carbon dioxide started too early,leading to an early loss of oxygen functionalities of the carbon source.An early loss of oxygen functionalities, however, appears to correlatewith an agglomeration of metal components and a segregation of metalprecursor and carbon source, ultimately yielding an irregulardistribution of large size metal clusters within the carbon matrix.Without wanting to be bound by theory, thus, it appears that sufficientavailability of oxygen containing functional groups during parts of thedrying procedure appears to be essential for fixing metal precursorswithin the carbon source in a highly dispersed and regular manner.

It was, furthermore, found that thermo-treating intermediate product Pat temperatures below 200° C. and above 380° C. did not yield grains ofnon-graphitizing carbon according to the invention with ironnanoparticles dispersed therein. In particular, it was found that theproportion of the non-graphitizing carbon phase according to theinvention itself decreased when the temperatures selected forthermo-treating were too high. These phases, however, are putativelyrelated to expedient hydrogen conductivity which, in turn, is essentialfor efficiently catalyzing reactions involving the conversion ofhydrogen. If on the other hand, temperatures selected forthermo-treating were too low or the duration of thermo-treating was tooshort, the level of residual oxygen in the carbon phase obtained was toohigh and reduction of metal precursors remained incomplete, leading tolowered catalytic activity as a result.

It should be noted, in addition, that, in view of the prior art,formation of the non-graphitizing carbon phase of the invention, as aresult of the process of the present invention, may appear to besurprising. However, without wanting to be bound by theory, it isassumed that formation of non-graphitizing carbon under low temperatureconditions of the process of the present invention, is facilitated bythe presence of high concentrations of metal precursors in a highlydispersed manner in intermediate product P before subsequentthermo-treating.

The process of the invention yields non-graphitizing carbon material ingranular form. Non-graphitizing carbon can be identified by a person ofskill using TEM-analysis (cf. P. W. Albers, Neutron scattering study ofthe terminating protons in the basic structural units ofnon-graphitizing and graphitizing carbons, Carbon 109 (2016), 239-245,page 241, figure 1c).

Experimental results obtained in conjunction with the present inventionindicate that catalytic activity of material obtained by the process ofthe invention, correlates well with its content of grains ofnon-graphitizing carbon exhibiting the features of the invention.

Typically, 90% of the non-graphitizing carbon grains obtained by theprocess of the present invention exhibit moderate size, i.e. diametersbetween 2 μm and 200 μm. It was presently found that, generally, morethan 95% of those moderately sized non-graphitizing carbon grains,obtained by the process of the present invention, contain ironnanoparticles dispersed therein that conform to the relation 4.5d_(p)/ω>D≥0.25 d_(p)/ω (with d_(p) denoting the average diameter of ironnanoparticles in the non-graphitizing carbon grains, D, denoting theaverage distance between iron nanoparticles in the non-graphitizingcarbon grains, and ω, denoting the combined total mass fraction of metalin the non-graphitizing carbon grains). The process of the presentinvention, typically, yields grains wherein, only the fraction of verysmall and the fraction of very large grains, i.e. the particle-fractionsoutside of the moderate size range between 2 μm and 200 μm, containsignificant portions of grains wherein iron nanoparticles do not conformto the relation 4.5 d_(p)/ω>D≥0.25 d_(p)/ω. Accordingly, the process ofthe present invention, generally, yields materials with a high contentof grains containing iron nanoparticles, wherein iron nanoparticlesconform to the relation 4.5 dp/ω>D≥0.25 d_(p)/ω. However, materials withlower contents of these grains may be obtained by other processes ordilution with other materials and are thus comprised by the presentinvention as well.

Accordingly, in a preferred embodiment the present invention relates tocatalytically active material, comprising grains of non-graphitizingcarbon with iron nanoparticles dispersed therein, wherein ironnanoparticles in more than 90% of moderately sized non-graphitizingcarbon grains, i.e. non-graphitizing carbon grains with a diameterbetween 2 μm and 200 μm conform to the relation 4.5 dp/ω>D≥0.25 dp/ω,and wherein further dp, the average diameter of iron nanoparticles inthe non-graphitizing carbon grains, is in the range of 1 nm to 20 nm, D,the average distance between iron nanoparticles in the non-graphitizingcarbon grains, is in the range of 2 nm to 150 nm, and w, the combinedtotal mass fraction of metal in the non-graphitizing carbon grains, isin the range of 30 wt % to 70 wt % of the total mass of thenon-graphitizing carbon grains.

In another preferred embodiment, the present invention relates tocatalytically active material, comprising grains of non-graphitizingcarbon with iron nanoparticles dispersed therein, wherein ironnanoparticles in more than 95% of moderately sized non-graphitizingcarbon grains, i.e. non-graphitizing carbon grains with a diameterbetween 2 μm and 200 μm conform to the relation 4.5 dp/ω>D≥0.25 dp/ω,and wherein further dp, the average diameter of iron nanoparticles inthe non-graphitizing carbon grains, is in the range of 1 nm to 20 nm, D,the average distance between iron nanoparticles in the non-graphitizingcarbon grains, is in the range of 2 nm to 150 nm, and w, the combinedtotal mass fraction of metal in the non-graphitizing carbon grains, isin the range of 30 wt % to 70 wt % of the total mass of thenon-graphitizing carbon grains.

The iron nanoparticles in the non-graphitizing carbon material of theinvention are mainly composed of elementary iron but may also contain,for example, iron oxide and/or dopant metal and/or secondary metal.

Computer aided analysis of TEM-pictures (TEM=transmission electronmicroscopy) coupled with Degussa derived TGZ method allows to determinediameters of individual iron nanoparticles as well as statisticalmeasures of sets thereof (cf. Parker et al. “The effect of particlesize, morphology and support on the formation of palladium hydride incommercial catalysts” Chemical Science, 2019, 10, 480).

In the context of the present invention, the average diameter of ironnanoparticles, d_(p), and the average distance D is determined by theTGZ-TEM method, as described in the following:

1. Sample Preparation

In most cases, the samples to be tested are available as powders.

The powders are usually dispersed in solvents under ultrasonicapplication. The ultrasonic application breaks down agglomerates intoaggregates and the result is an aggregate distribution rather than amixture of aggregates and agglomerates. A micro pipette is then used todrop a drop onto a film-coated mesh lying on a piece of filter paper.The excess liquid is quickly sucked off through the filter paper so thatagglomerate formation is prevented by the drying process. The suspendedgrains must not be too dense, as the shape and outline of thenanoparticles cannot be clearly seen through contact and overlapping ofgrains. An optimal dilution must be determined by test experiments witha dilution series.

In general, it can be stated that the type of preparation has hardly anyeffect on the result of the primary nanoparticle size evaluation.

2. Performance of the Test

The individual nanoparticles to be characterized on the basis of the TEMimages must be imaged with sufficiently sharp contours.

A distribution of the nanoparticles that is not too dense with fewoverlaps or particles that are as separated from each other as possibleon the TEM images facilitates the measurement on the TGZ3, but does notinfluence the measurement result.

After examining various image sections of a TEM preparation, suitableareas are selected accordingly. It should be noted that the ratio ofsmall, medium and large nanoparticles for the respective sample isrepresentative and characteristic and no selective preference of smallor large particles is given by the operator.

The total number of primary nanoparticles to be measured depends on thescattering range of the primary nanoparticle size: the larger thescattering range, the more particles have to be measured to obtain anadequate statistical statement. For metal catalysts approx. 1500 singleparticles are measured. For all TGZ analysis a calibrated Hitachi H-7500field transmission electron microscope operated at 100 keV, equippedwith a CCD-Camera was used.

3. Description of the Measurement Procedure

The measurement procedure is done according to the TGZ3 manual by CarlZEISS (“Teilchengröβenanalysator (particle size analyser) TGZ3”; ManualFa. Carl ZEISS).

4. Measurement Data Processing

A detailed description of the measurement data processing is given in(F. Endter u. H. Gebauer, “Optik (Optics)” 13 (1956), 97) and (K.Seibold and M. Voll, “Distribution function for describing the particlesize distribution of Soot and pyrogenic oxides”. Chemiker-Zeitung, 102(1978), Nr. 4, 131-135).

The statistical summary is compiled in the form of a report. A detailedstatistical description is given in (Lothar Sachs, “Statisticalmethods”, 5. Auflage, Springer-Verlag, Berlin (1982)).

5. Evaluation and Display of Results

-   -   a. Total number of particles (N)    -   b. Particle size distributions q0(x) and q3(x) evaluated of 1500        isolated nanoparticles per sample    -   c. Particle diameter d_(n), mean diameter (d_(n))

$d_{n} = {\frac{\sum{n_{i}d_{i}}}{\sum n_{i}} = \frac{\sum{n_{i}d_{i}}}{n}}$

-   -   -   n_(i)=number of particles with diameter d_(i)

    -   d. Average distance D on rectangular plane

$D = {\frac{1}{a^{2}b^{2}}{\int_{0}^{b}{{dy}^{*}{\int_{0}^{b}{{dy}{\int_{0}^{a}{{dx}^{*}{\int_{0}^{a}{\sqrt{\left( {x^{*} - x} \right)^{2} + \left( {y^{*} - y} \right)^{2}}{dx}}}}}}}}}}$

-   -   -   a, b=length, width of the rectangular plane        -   x, y, x*, y*=particle coordinates.

The combined total mass fraction of metal, w, is defined as the fractionof the combined total masses of iron and all dopant and secondarymetals, of the total mass of the material under consideration:ω=(m(iron)+m(dopant metals)+m(secondary metals))/m(material); withm(iron)=total mass of iron in elemental form contained in the materialin the form of elemental iron itself and/or in the form of any compoundsof iron, m(dopant metals)=combined total mass of all dopant metals inelemental form contained in the material in the form of the elementaldopant metals themselves and/or in the form of any compounds of thedopant metals, m(secondary metals)=combined total mass of all secondarymetals in elemental form contained in the material in the form of theelemental secondary metals themselves and/or in the form of anycompounds of the secondary metals, and m(material)=total mass ofmaterial under consideration.

The combined total mass fraction of metal, w, can be determined by meansof all methods for quantitative elementary analysis, in particular XRF(X-ray fluorescence) and ICP-AES (Inductively coupled plasma atomicemission spectroscopy).

A suitable choice of conditions in the process according to the presentinvention allows to control the combined total mass fraction of metal,w, in the material obtained:

Processes providing in step (a), solutions with a high metal content(iron and dopant and secondary metals combined), yield materials with ahigher combined total mass fraction of metal, w, than processesproviding in step (a) solutions with a lower metal content.

Processes with thermo-treating in step (c) at high temperatures in therange from 200° C. to 380° C. yield materials with a higher combinedtotal mass fraction of metal, w, than processes with thermo-treating instep (c) at lower temperatures.

The process of the present invention yields granular material. The sizeof individual particles of this material as well as statistical measuresof sets thereof can be determined by means of laser diffraction analysis(e.g. Cilas 1190 Series), well known to persons of skill in this field.

Typically, the process of the present invention yields granular materialexhibiting the following particle size distribution: d10=5 μm, d50=40μm, d90=150 μm.

In view of the fact that material obtained by the process according tothe present invention was found to be very suitable for manufacturingshaped catalysts, in a preferred embodiment the present inventionrelates to catalytically active material, comprising grains ofnon-graphitizing carbon with iron nanoparticles dispersed therein,

-   -   wherein    -   d_(p), the average diameter of iron nanoparticles in the        non-graphitizing carbon grains, is in the range of 1 nm to 20        nm,    -   D, the average distance between iron nanoparticles in the        non-graphitizing carbon grains, is in the range of 2 nm to 150        nm, and    -   ω, the combined total mass fraction of metal in the        non-graphitizing carbon grains, is in the range of 30 wt % to 70        wt % of the total mass of the non-graphitizing carbon grains,    -   and wherein    -   d_(p), D and ω conform to the following relation:

4.5d _(p) /ω>D≥0.25d _(p)/ω,

-   -   and wherein    -   the non-graphitizing carbon grains exhibit the following        particle size distribution: d10=5 μm, d50=40 μm, d90=150 μm.

There may be applications for materials according to the presentinvention, where the presence of Nitrogen is detrimental. Accordingly,in a preferred embodiment, the present invention relates to materialaccording to the invention wherein the total mass fraction of nitrogenis less than 1 wt % of the total mass of the material.

Experimental results indicate, that material with relatively small ironnanoparticles may exhibit particularly attractive catalytic properties.Accordingly, in a preferred embodiment, the present invention relates tomaterial according to the invention wherein d_(p) is in the range of 4nm to 18 nm. In a particularly preferred embodiment, the presentinvention relates to material according to the invention wherein d_(p)is in the range of 6 nm to 14 nm.

As indicated by experimental results, addition of dopant metals affectscatalytic activity of the materials of the present invention.Accordingly, in a preferred embodiment, the present invention relates tomaterial according to the invention wherein the iron nanoparticles havebeen doped with dopant metal, and wherein the dopant metal is selectedfrom Na (sodium) or K (potassium) or Ca (calcium) or Mg (magnesium) ormixtures thereof, and wherein the material exhibits a molar ratioRDM=n(iron):n(dopant metal) in the range of 5 to 1000.

In a particularly preferred embodiment, the present invention relates tomaterial according to the invention wherein the iron nanoparticles havebeen doped with dopant metal, and wherein the dopant metal is selectedfrom Na (sodium) or K (potassium) or Ca (calcium) or Mg (magnesium) ormixtures thereof, and wherein the material exhibits a molar ratioRDM=n(iron):n(dopant metal) in the range of 10 to 500.

In another preferred embodiment, the present invention relates tomaterial according to the invention wherein the iron nanoparticles havebeen combined with a secondary metal, and wherein the secondary metal isselected from group 1 or group 2,

with group 1 defined as: Mo (molybdenum) or W (tungsten) or mixturesthereof, and

with group 2 defined as: Co (cobalt) or Cu (copper) or Mn (manganese) ormixtures thereof,

and wherein the material exhibits a molar ratio RSM=n(iron):n(secondarymetal) in the range of 1 to 50.

The present invention, further, relates to a process for the manufactureof the materials of the invention. As indicated above, a combination oftwo process steps was found to be crucial:

-   -   (i) spray drying or freeze drying of the aqueous solution of        metal precursor and organic carbon source, and    -   (ii) thermal treatment at moderate temperatures of the resulting        intermediate.

Accordingly, in another aspect, the present invention is, further,directed at a process for the manufacture of material according to theinvention, comprising the following steps:

-   -   (a) providing an aqueous solution comprising metal precursor and        organic carbon source,        -   wherein the metal precursor comprises one or a combination            of more than one organic, at least partially water soluble,            salts of iron, and        -   wherein the organic carbon source is one or a combination of            more than one saturated, aliphatic di-, tri-, or            polycarboxylic acids,    -   (b) spray drying or freeze drying the aqueous solution of metal        precursor and organic carbon source and, thus, obtaining        intermediate product P,    -   (c) thermo-treating intermediate product P at a temperature in        the range from 200° C. to 380° C.

Each of the process steps may be performed in a batch-wise or continuousformat.

In another aspect the present invention is, further, directed atmaterials obtainable by the process of the invention.

As indicated above, formation of the materials of the present inventionrequires a combination of spray drying or freeze drying and suitablethermal treatment at moderate temperatures. Accordingly, it appearsreasonable to assume that only material present in solution, i.e. indissolved form in the solution provided in step (a) of the process, canbe transformed into material according to the invention. However,undissolved matter in solid form may be suspended in solution providedin step (a) as long as it does not interfere with the process formingthe material of the present invention. Such solids, which may, forexample, originate from undissolved metal precursor or organic carbonsource, may form solid diluents of the material of the invention in thesolid product obtained after step (c) of the process of the invention.Similarly, organic solvents may be dissolved or emulsified in thesolution provided in step (a) as long as their presence does notinterfere with the process forming the material of the presentinvention. However, in order to avoid interference with the processforming the material of the present invention, in preferred embodiments,the process of the invention is performed with aqueous solutions,provided in step (a), that are free of undissolved matter in solid formas well as free of organic solvents.

If no dopant metal and no secondary metal is used, the metal precursorin the solution provided in step (a) of the process of the presentinvention, is one or a combination of more than one organic, at leastpartially water soluble, salts of iron. In the present context a salt isconsidered as being at least partially water soluble, if at least afraction of the salt dissolves in the aqueous solution provided in step(a) under the conditions employed in the process. Preferably, if nodopant metal is used and no secondary metal is used, the metal precursorin the solution provided in step (a) of the process of the presentinvention, is one or a combination of more than one, organic salts ofiron, whereof the amounts desired to be included into the solution arecompletely soluble in the aqueous solution of step (a).

In a preferred embodiment of the present invention no dopant metal andno secondary metal is used.

In another preferred embodiment of the present invention dopant metal isused but no secondary metal is used.

If dopant metal is used, the metal precursor in the solution provided instep (a) of the process of the present invention is a combination of oneor more organic, at least partially water soluble, salts of iron, withone or more organic, at least partially water soluble, salts of one ormore dopant metals. Preferably, if dopant metal is used, the metalprecursor in the solution provided in step (a) of the process of thepresent invention, is a combination of one or more organic salts of ironwith one or more organic salts of one or more dopant metals, whereof theamounts desired to be included into the solution are completely solublein the aqueous solution of step (a).

If secondary metal is used, the metal precursor in the solution providedin step (a) of the process of the present invention is a combination ofone or more organic, at least partially water soluble, salts of iron,with one or more organic, at least partially water soluble, salts of oneor more secondary metals. Preferably, if secondary metal is used, themetal precursor in the solution provided in step (a) of the process ofthe present invention, is a combination of one or more organic salts ofiron with one or more organic salts of one or more secondary metals,whereof the amounts desired to be included into the solution arecompletely soluble in the aqueous solution of step (a).

If dopant and secondary metal is used, the metal precursor in thesolution provided in step (a) of the process of the present invention isa combination of one or more organic, at least partially water soluble,salts of iron, with one or more organic, at least partially watersoluble, salts of one or more dopant metals and one or more organic, atleast partially water soluble, salts of one or more secondary metals.Preferably, if dopant and secondary metal is used, the metal precursorin the solution provided in step (a) of the process of the presentinvention, is a combination of one or more organic salts of iron withone or more organic salts of one or more dopant metals and one or moreorganic, at least partially water soluble, salts of one or moresecondary metals, whereof the amounts desired to be included into thesolution are completely soluble in the aqueous solution of step (a).

Preferred organic anions of the metal precursors in the solutionprovided in step (a) of the process of the present invention areacetate, carbonate, oxalate, citrate, malonate, tartrate and glutarate.If nitrogen does not need to be avoided, nitrate is another preferredanion of the metal precursors in the solution provided in step (a).

Saturated, aliphatic di-, tri-, or polycarboxylic acids, alone or aspart of a mixture, may be used as organic carbon sources of the aqueoussolution provided in step (a), as long as they support formation of thematerials of the present invention. In preferred embodiments, malonicacid, glutaric acid, citric acid or mixtures thereof are used as organiccarbon source of the aqueous solution provided in step (a) of theprocess of the present invention. In a particularly preferred embodimentof the present invention, citric acid is used as organic carbon sourceof the aqueous solution provided in step (a) of the process of thepresent invention.

The aqueous solution provided in step (a) is spray dried or freeze driedin step (b) of the process of the present invention. The productobtained therefrom is referred to as intermediate product P in thecontext of the present invention. Process parameters for spray dryingand freeze drying can be varied over a wide range as long as the dryingprocess is performed without interruption and the combined content ofwater and organic solvents exhibited by intermediate product P, is below10 wt %. In a preferred embodiment of the present invention the aqueoussolution provided in step (a) is spray dried in step (b) of the processof the present invention.

Thermo-treating according to step (c) of the process of the presentinvention is performed under defined temperature conditions and inertgas atmosphere, e.g. nitrogen, or air. A wide range of suitable furnacesfor this purpose is available commercially. In preferred embodiments,thermo-treating is performed under inert gas atmosphere, e.g. nitrogen.Heating rates during thermo-treating should be small enough to allowhomogeneous distribution of heat, i.e. typically smaller than 15 K/min,preferably smaller than 10 K/min, and particularly preferred smallerthan 5 K/min. Thermo treating intermediate product P is performed at atemperature in the range from 200° C. to 380° C. In preferredembodiments of the present invention, thermo treating intermediateproduct P is performed at a temperature in the range from 255° C. to375° C. In particularly preferred embodiments, thermo-treatingintermediate product P is performed at a temperature in the range from300° C. to 350° C. Typically, thermo treating intermediate product P isperformed for a duration of 1 to 4 hours, but thermo-treating for longeror shorter intervals of time may work as well. Heating and coolingintervals are not accounted for when determining the duration of thermotreating. In preferred embodiments thermo-treating intermediate productP is performed for a duration of 1 to 4 hours.

As indicated above, materials according to the present invention exhibitcatalytic activity. Accordingly, in another aspect, the presentinvention, further, relates to the use of materials of the presentinvention as catalysts.

Materials according to the present invention can be used, for example,as catalysts in liquid phase hydrogenations of organic compounds,specifically unsaturated compounds like alkenes and alkynes, aldehydesand ketones, esters and imines, nitro compounds and nitriles. Materialsaccording to the present invention are, further, very active catalystsfor the reductive amination of carbonyl compounds. Accordingly, inanother aspect, the present invention, further, relates to the use ofmaterials of the invention as catalysts for the hydrogenation of organiccompounds and/or the reductive amination of carbonyl compounds.

Materials according to the present invention can also be used ascatalysts in the conversion of carbon monoxide, carbon dioxide ormixtures thereof, with hydrogen, to alkenes, alkanes or mixturesthereof. Accordingly, in another aspect, the present invention, further,relates to the use of materials of the invention as catalysts for theconversion of carbon monoxide, carbon dioxide or mixtures thereof withhydrogen, to alkenes, alkanes or mixtures thereof.

Materials according to the present invention may be used as catalysts inunmodified form or may be transformed into catalyst bodies by shapingprocesses (e.g. tableting, pelletizing, extrusion, coating,3D-printing), well known to persons of skill in the art.

EXAMPLES Examples Fe a,b—Preparation of Carbon Embedded Fe-Nanoparticles

Carbon embedded Fe-nanoparticles were prepared by dissolving 14.4 gcitric acid (puriss, Sigma Aldrich) in 75 mL of deionized water underconstant stirring at room temperature. In a second beaker 18.7 gIron(II)-acetate (Fe(CH₃COO)₂, Sigma Aldrich) was dissolved in 75 mL ofdeionized water under constant stirring at room temperature. TheIron-acetate solution was slowly added to the citric acid solution andstirred for another 30 min at room temperature. The resultant solutionwas spray dried using a conventional mini spray dryer (Büchi, Mini SprayDryer B-290) with constant inlet temperature of 220° C., outlettemperature of 120° C. and 20% pump speed. The obtained powder was splitinto two fractions with identical mass for the final thermo-treatment.

The first sample was thermo-treated in a tubular furnace under nitrogenatmosphere, with a 180 min ramp to 300° C., where temperature wasmaintained for another 4 h followed by natural cooling down. Theresultant catalyst powder was labeled FeCat. 1a.

The second sample was thermo-treated in a similar fashion under nitrogenatmosphere. The sample was heated up to 350° C. within 180 min wheretemperature was maintained for 4 h followed by natural cool down. Theresultant catalyst powder was labeled FeCat. 1b.

The materials exhibit the following characteristics which weredetermined by XRF (X-ray fluorescence) and TGZ analysis using acalibrated Hitachi H-7500 field transmission electron microscopeoperated at 100 keV, equipped with a CCD-Camera:

ID d_(p) ω D FeCat. 1a 10 nm 0.56 17 nm FeCat. 1b 12 nm 0.61 14 nm

Comparative Examples

For comparison a highly loaded catalyst with 20 wt % Iron on aconventional Vulcan XC72R Carbon support was prepared by means ofincipient wetness impregnation and is labeled as FeCat. Ref.

The materials exhibit the following characteristics which weredetermined by XRF (X-ray fluorescence) and TGZ analysis using acalibrated Hitachi H-7500 field transmission electron microscopeoperated at 100 keV, equipped with a CCD-Camera:

ID d_(p) ω D FeCat. Ref 72 nm 0.20 n.d.*

Testing Catalytic Activity

Experiments to determine Catalytic activity and selectivity of thematerials were performed in a batch-wise fashion using 200 mg ofcatalyst and 5 mmol of substrate in 5 ml of methanol. Autoclaves wereheated to the desired reaction temperature and agitated under a constanthydrogen pressure of 50 bar for all experiments. Reaction products werefiltered and analyzed by means of GC-MS.

I. Hydrogenation of N-Benzylidene-Benzylamine

Duration Temp T Reactant product side-product ID Cat. ID h ° C. % % % 1FeCat. 1 a 20,00 100,00 66,1 29,5  4,40 2 FeCat. 1 b 20,00 100,00 64,031,9  4,10 3 FeCat. Ref 20,00 100,00 89,8 0 10,2

II. Hydrogenation of Methyl Crotonate to Methyl Butyrate

Duration Temp. T reactant product ID Cat. ID h ° C. % % 4 FeCat. 1 a20,00 80,00  5,00  95,00 5 FeCat. 1 b 20,00 80,00  0,00 100,00 6 FeCat.Ref 20,00 80,00 38,7  61,3

III. Hydrogenation of Dodecannitrile

ID Cat. ID Duration h Temp. T ° C. Reactant % product % side-product % 7FeCat. 1 a 20,00 80,00 85,9  7,60  6,40 8 FeCat. 1 b 20,00 80,00 73,016,7 10,3 9 FeCat. Ref 20,00 80,00 98,0  0,00  2,00

IV. Hydrogenation of Acetylnaphthalene

ID Cat. ID Duration h Temp. T ° C. Reactant % product % side-product %10 FeCat. 1 a 20,00 80,00  62,6 37,4 0,00 11 FeCat. 1 b 20,00 80,00 51,6 48,4 0,00 12 FeCat. Ref 20,00 80,00 100,0  0,00 0,00

1-14. (canceled)
 15. Catalytically active material, comprising grains ofnon-graphitizing carbon with iron nanoparticles dispersed therein,wherein: d_(p), the average diameter of iron nanoparticles in thenon-graphitizing carbon grains, is in the range of 1 nm to 20 nm; D, theaverage distance between iron nanoparticles in the non-graphitizingcarbon grains, is in the range of 2 nm to 150 nm; and ω, the combinedtotal mass fraction of metal in the non-graphitizing carbon grains, isin the range of 30 wt % to 70 wt % of the total mass of thenon-graphitizing carbon grains; wherein d_(p) and D are measured byTGZ-TEM, and d_(p), D and ω conform to the following relation: 4.5d_(p)/ω>D≥0.25 d_(p)/ω.
 16. The catalytically active material of claim15, wherein the non-graphitizing carbon grains exhibit the followingparticle size distribution: d10=5 μm, d50=40 μm, and d90=150 μm.
 17. Thecatalytically active material of claim 15, wherein the total massfraction of nitrogen in the non-graphitizing carbon grains is less than1 wt % of the total mass of the non-graphitizing carbon grains.
 18. Thecatalytically active material of claim 15, wherein d_(p) is in the rangeof 4 nm to 18 nm.
 19. The catalytically active material of claim 15,wherein d_(p) is in the range of 6 nm to 14 nm.
 20. The catalyticallyactive material of claim 15, wherein the catalytically active materialmaterial has been doped with a dopant metal, selected from the groupconsisting of: Na (sodium); K (potassium); Ca (calcium); Mg (magnesium);and mixtures thereof, and wherein the non-graphitizing carbon grainsexhibit a molar ratio RDM=n(iron):n(dopant metal) in the range of 5 to1000.
 21. The catalytically active material of claim 15, wherein thematerial has been combined with a secondary metal, selected from group 1or group 2, wherein the metal of group 1 is selected from the groupconsisting of: Mo (molybdenum); W (tungsten); and mixtures thereof, andthe metal of group 2 is selected from the group consisting of: Co(cobalt); Cu (copper); Mn (manganese); and mixtures thereof, and whereinthe non-graphitizing carbon grains exhibit a molar ratioRSM=n(iron):n(secondary metal) in the range of 1 to
 50. 22. Thecatalytically active material of claim 16, wherein the total massfraction of nitrogen in the non-graphitizing carbon grains is less than1 wt % of the total mass of the non-graphitizing carbon grains.
 23. Thecatalytically active material of claim 16, wherein d_(p) is in the rangeof 4 nm to 18 nm.
 24. The catalytically active material of claim 16,wherein the catalytically active material material has been doped with adopant metal, selected from the group consisting of: Na; K; Ca; Mg; andmixtures thereof, and wherein the non-graphitizing carbon grains exhibita molar ratio RDM=n(iron):n(dopant metal) in the range of 5 to
 1000. 25.The catalytically active material of claim 16, wherein the catalyticallyactive material has been combined with a secondary metal, selected fromgroup 1 or group 2, wherein the metal of group 1 is selected from thegroup consisting of: Mo; W; and mixtures thereof, and the metal of group2 is selected from the group consisting of: Co; Cu; Mn; and mixturesthereof, and wherein the non-graphitizing carbon grains exhibit a molarratio RSM=n(iron):n(secondary metal) in the range of 1 to
 50. 26. Thecatalytically active material of claim 17, wherein the catalyticallyactive material has been combined with a secondary metal, selected fromgroup 1 or group 2, wherein the metal of group 1 is selected from thegroup consisting of: Mo; W; and mixtures thereof, and the metal of group2 is selected from the group consisting of: Co; Cu; Mn; and mixturesthereof, and wherein the non-graphitizing carbon grains exhibit a molarratio RSM=n(iron):n(secondary metal) in the range of 1 to
 50. 27. Thecatalytically active material of claim 26, wherein d_(p) is in the rangeof 4 nm to 18 nm.
 28. A process for the manufacture of the catalyticallyactive material of claim 15, comprising of the following steps: (a)providing an aqueous solution comprising a metal precursor and anorganic carbon source, wherein: the metal precursor comprises one ormore organic, at least partially water soluble, salts of iron; and theorganic carbon source comprises one or more saturated, aliphatic di-,tri-, or polycarboxylic acids; (b) spray drying or freeze drying theaqueous solution of the metal precursor and the organic carbon source,and thus obtaining intermediate product P; (c) thermo-treatingintermediate product P at a temperature in the range from 200° C. to380° C.
 29. The process of claim 28, wherein the organic carbon sourceis selected from the group consisting of: malonic acid; tartaric acid;citric acid; and mixtures thereof.
 30. The process of claim 28, whereinintermediate product P is thermo-treated at a temperature in the rangefrom 255° C. to 375° C. for 1 to 4 hours.
 31. The process of claim 28,wherein intermediate product P is thermo-treated at a temperature in therange from 300° C. to 350° C. for 1 to 4 hours.
 32. A chemical reactioncomprising the catalytically active material of claim 15 as a catalyst.33. The chemical reaction of claim 32, wherein the catalyst catalysesthe hydrogenation of organic compounds and/or the reductive amination ofcarbonyl compounds.
 34. The chemical reaction of 32, comprising reactingcarbon monoxide, carbon dioxide or mixtures thereof, with hydrogen, toform alkenes, alkanes or mixtures thereof.